Composite structural material, and method of producing the same

ABSTRACT

A plate-shaped composite material has a first member and a second member. The first member is an expanded metal formed of a metal plate. The coefficient of linear expansion of the metal plate is less than or equal to 8×10 −6 /degrees Celsius. The first member suppresses thermal expansion of the composite material. The coefficient of thermal conductivity of the second member is greater than or equal to 200 W/(m×K). The second member maintains the coefficient of thermal conductivity of the composite material. This structure provides a reliable coefficient of thermal conductivity and high strength. The structure is suitable for a cooling substrate on which electronic elements such as semiconductors are mounted.

TECHNICAL FIELD

[0001] The present invention relates to a composite material and amanufacturing method of the composite material. More specifically, thepresent invention pertains to a composite material that is suitable fora cooling substrate on which electronic elements, such assemiconductors, are mounted, or a composite material that is suitablefor wiring material of semiconductors. The present invention alsopertains to manufacturing methods of the composite materials.

BACKGROUND ART

[0002] Typical electronic elements such as semiconductors generate heatwhen supplied with electric current. The electronic elements are cooledto prevent the performance from deteriorating.

[0003] Packaging methods of a semiconductor include the use of a heatsink. FIG. 16 shows an aluminum base 41, which constitute a casing, anda heat sink 42, which is secured to the aluminum base 41 by screws (notshown) or by soldering. An insulated-substrate 43 is secured to the heatsink 42 by soldering. The insulated-substrate 43 has metal (A1) layers43 a on both sides. An electronic element 44, such as a semiconductor,is mounted on one of the metal layers 43 a of the insulated-substrate 43by soldering. The insulated-substrate 43 is made of aluminum nitride(AlN). The heat sink 42 uses material having low coefficient of thermalexpansion and high coefficient of thermal conductivity. The material maybe metal matrix composite material having a metal matrix phase to whichceramics are dispersed. The metal matrix composite material may be, forexample, an aluminum substrate to which silicon carbide (Sic) particlesare dispersed.

[0004] The metal matrix composite material used for the heat sink 42 isexpensive and has low workability. Therefore, a different coolingsubstrate that is inexpensive and has high workability has beenproposed. For example, Japanese Laid-Open Patent Publication No. 6-77365discloses a cooling substrate 47, which is integrally formed with metalplates 46 and a wire fabric 45 as shown in FIGS. 17(a) and 17(b). Themetal plates 46 are made of copper, copper and tungsten, or copper andmolybdenum. The wire fabric 45 is woven with thin metal wires made ofmolybdenum or tungsten. The metal plates 46 are laid on one another withthe wire fabric 45 arranged in between. In this state, the metal plates46 and the wire fabric 45 are heated and rolled. This integrates themetal plates 46 and the wire fabric 45 and forms a laminated sheet ofthe cooling substrate 47.

[0005] Japanese Laid-Open Patent Publication No. 7-249717 discloses acooling substrate that is formed by integrating a wire fabric made ofthin metal wires of molybdenum or tungsten with impregnant containingcopper, copper and tungsten, or copper and molybdenum.

[0006] Japanese Laid-Open Patent Publication No. 6-334074 discloses asubstrate for semiconductors as shown in FIG. 18. The substrate includesa base material 48, in which holes 48 a are formed. The base material 48is made of metal or alloy, the coefficient of thermal expansion of whichis less than or equal to 8×10⁻⁶/degrees Celsius. The holes 48 a arefilled with highly thermal conductive material made of metal or alloy,the coefficient of thermal conductivity of which is greater than orequal to 210 W/(m×K). The highly thermal conductive material may be Cu,Al, Ag, Au or an alloy that mainly includes Cu, Al, Ag, or Au. The basematerial 48 may be an invar alloy, which contains 30 to 50% Ni by weightand Fe making up the remaining proportion, or a super invar alloy, whichincludes Co. The holes 48 a of the base material 48 are made by punchingafter processing the raw material into flat shape, or the holes 48 a areformed during casting by the precision casting (lost-wax process).

[0007] In a semiconductor, a silicon chip (silicon element) needs to beconnected to other electrode directly or via a pad located on thesilicon chip with wiring. In general, wiring material, such as aluminumwire, is used for wiring. However, when the wiring material is used, theelement might be damaged during wire bonding. Further, when thetemperature is increased due to heat generation during operation of thesemiconductor, joint portions might be deteriorated or disconnected bythe thermal stress caused by the difference between the thermalexpansion of the wire and the silicon element.

[0008] To solve the above mentioned problem, Japanese Patent PublicationNo. 3216305 discloses a semiconductor having bonding pads. The bondingpads are located on a semiconductor layer, which serves as an activeregion of a semiconductor element. The bonding pads are electricallyconnected to electrodes outside the silicon element. The bonding pads ofthe semiconductor are connected to each other with plate-shapedconductive members.

[0009] When the cooling substrate 47 shown in FIG. 17(b) is rolled,spaces Δ are easily formed at portions where the thin metal wires 45 aof the wire fabric 45 overlap with each other and in the vicinity of theoverlapped portions as shown in FIG. 19, which is an enlarged partialcross sectional view of FIG. 17(b). As a result, air in the space Δdeteriorates the heat conductivity. Also, cracks are easily formed inthe wire fabric 45 at the spaces Δ by the repeated thermal expansion andthermal contraction, which reduces the strength. To improve the strengthof the wire fabric 45, the contact points of the thin metal wires 45 amay be welded. However, it is difficult to weld the contact points ofthe wire fabric 45, since the wire fabric 45 is woven with the thinmetal wires 45 a and has fine mesh.

[0010]FIG. 20(b) illustrates a cooling substrate 51 according to anotherprior art. The cooling substrate 51 includes a flat metal plate 49. Themetal plate 49 includes partitions 49 b, which are arranged atpredetermined intervals. Holes 49 a are defined between the adjacentpartitions 49 b. The metal plate 49 is covered with a metal 50, whichhas higher coefficient of thermal expansion than the metal plate 49.

[0011] It is required to maximize the volumetric proportion of metalhaving low coefficient of thermal expansion to suppress the coefficientof thermal expansion of the cooling substrate. To suppress thecoefficient of thermal expansion of the cooling substrate 47 shown inFIGS. 17(a), 17(b), 19, and 20(a), the wire fabric 45, which is wovenwith the thin metal wires 45 a having low coefficient of thermalexpansion, is used. However, when rolling, the metal plates 46, whichhave higher coefficient of thermal expansion than the thin metal wires45 a, cover the wire fabric 45 and enter portions 47 a (see FIG. 20(a))that correspond to bent portions of the thin metal wires 45 a inaddition to the meshes of the wire fabric 45. On the other hand, in thecase with the cooling substrate 51 shown in FIG. 20(b), the metal 50enters the holes 49 a that correspond to the mesh of the wire fabric 45shown in FIG. 20(a) and around the longitudinal ends of the metal plates49. The longitudinal ends of each metal plate 49 are flat. Therefore,the metal that corresponds to the metal plates 46 that exist at theportions 47 a shown in FIG. 20(a) does not exist in the coolingsubstrate 51 shown in FIG. 20(b). That is, the proportion of metalhaving high coefficient of thermal expansion in the cooling substrate 47shown in FIG. 20(a) is greater than in the case with the coolingsubstrate 51 shown in FIG. 20(b) by the amount corresponding to the bentportions.

[0012] In the case where holes are formed by punching after processing araw material into flat shape as the substrate for semiconductors shownin FIG. 18, the yield rate decreases, which increases the material cost.Also, forming the holes by precision casting (lost wax) increases themanufacturing cost.

[0013] In the process disclosed in Japanese Patent Publication No.3216305, the difference between the coefficient of thermal expansion ofthe semiconductor element and the coefficient of thermal expansion ofthe plate-shaped conductive material is great. Thus, the thermal stresscaused by heat generation during operation of the semiconductor mightdisconnect the wiring of the plate-shaped conductive material.

DISCLOSURE OF THE INVENTION

[0014] Accordingly, it is a first objective of the present invention toprovide a high-strength inexpensive composite material that has areliable coefficient of thermal conductivity and is suitable for coolingsubstrate on which electronic elements, such as semiconductors, aremounted, and a method for manufacturing the composite material. A secondobjective of the present invention is to provide a composite materialthat is suitable for wiring material of semiconductors and a method formanufacturing the composite material.

[0015] To achieve the above objective, the present invention provides aplate-shaped composite material, which includes a first member and asecond member. The first member is an expanded metal made of metalplate. The coefficient of linear expansion of the metal plate is lessthan or equal to 8×10⁻⁶/degrees Celsius. The second member is formed ofmetal. The coefficient of thermal conductivity of the metal is greaterthan or equal to 200 W/(m×K). The first member suppresses thermalexpansion of the composite material. The second member maintains thecoefficient of thermal conductivity of the composite material.

[0016] The present invention also provides another composite material.The composite material includes a plate-shaped conductive member havingan end and a plate-shaped expansion suppressing portion located at theend of the conductive member. The expansion suppressing portion includesa first member and a second member. The first member is an expandedmetal made of metal plate. The coefficient of linear expansion of themetal plate is less than or equal to 8×10⁻⁶/degrees Celsius. The secondmember is formed of metal. The coefficient of thermal conductivity ofthe metal is greater than or equal to 200 W/(m×K). The first membersuppresses the thermal expansion of the composite material. The secondmember maintains the coefficient of thermal conductivity of thecomposite material.

[0017] The present invention also provides another composite material.The composite material includes a plate-shaped conductive member havingan end and a plate-shaped expansion suppressing portion located at theend of the conductive member. The expansion suppressing portion includesa first member and a second member. The first member is an expandedmetal made of metal plate. The coefficient of linear expansion of themetal plate is less than or equal to 8×10⁻⁶/degrees Celsius. The secondmember is formed of metal. The coefficient of thermal conductivity ofthe metal is greater than or equal to 200 W/(m×K). At least one of theconductive member and the second member is filled in meshes of the firstmember and laminated on the first member.

[0018] The present invention also provides another composite material.The composite material includes a plate-shaped conductive member havingan end and an expansion suppressing portion located at the end of theconductive member. The expansion suppressing portion includes aplate-shaped insulation member and an expanded metal made of a metalplate. The coefficient of linear expansion of the metal plate is lessthan or equal to 8×10⁻⁶/degrees Celsius. Part of the conductive memberis filled in meshes of the expanded metal.

[0019] The present invention also provides a manufacturing method of acomposite material. The method being characterized by: forming a firstmember from an expanded metal made of a metal plate, wherein thecoefficient of linear expansion of the metal plate is less than or equalto 8×10⁻⁶/degrees Celsius; and surrounding the first member with asecond member, wherein the second member is made of metal, and whereinthe coefficient of thermal conductivity of the metal is greater than orequal to 200 W/(m×K).

[0020] The present invention also provides another manufacturing methodof a composite material. The method being characterized by: laminatingan expanded metal and a rubber sheet at an end of a plate-shapedconductive member, wherein the expanded metal is formed of a metalplate, wherein the coefficient of linear expansion of the metal plate isless than or equal to 8×10⁻⁶/degrees Celsius, and wherein the expandedmetal suppresses thermal expansion of the composite material; applyingpressure to the rubber sheet and filling the conductive member and therubber sheet in meshes of the expanded metal; and surrounding theexpanded metal with a metal to maintain the coefficient of thermalconductivity of the composite material, wherein the coefficient ofthermal conductivity of the metal is greater than or equal to 200W/(m×K).

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1(a) is a schematic cross-sectional view illustrating acomposite material according to a first embodiment of the presentinvention;

[0022]FIG. 1(b) is a cross-sectional view taken along line 1 b-1 b inFIG. 1(a);

[0023]FIG. 2 is a schematic perspective view illustrating metal platesand an expanded metal, which constitute the composite material;

[0024]FIG. 3 is a schematic cross-sectional view illustrating amanufacturing method of the composite material of FIG. 1;

[0025]FIG. 4(a) is a schematic cross-sectional view illustrating amanufacturing method of a composite material according to a secondembodiment of the present invention;

[0026]FIG. 4(b) is a schematic cross-sectional view illustrating themanufacturing method of the composite material shown in FIG. 4(a);

[0027]FIG. 5(a) is a schematic cross-sectional view illustrating acomposite material according to a third embodiment;

[0028]FIG. 5(b) is a schematic cross-sectional view taken along line 5b-5 b in FIG. 5(a);

[0029]FIG. 6 is a schematic perspective view illustrating metal platesand an expanded metal forming the composite material shown in FIG. 5(a);

[0030]FIG. 7 is a schematic cross-sectional view illustrating amanufacturing method of the composite material shown in FIG. 5(a);

[0031]FIG. 8(a) is a schematic plan view illustrating a compositematerial according to a fourth embodiment;

[0032]FIG. 8(b) is a schematic cross-sectional view of FIG. 8(a);

[0033]FIG. 8(c) is a schematic plan view illustrating the compositematerial of FIG. 8(a) cut into the size of a wiring material;

[0034]FIG. 9 is a schematic side view illustrating a manufacturingmethod of the composite material shown in FIG. 8(a);

[0035]FIG. 10 is a schematic side view illustrating a manufacturingmethod different from the manufacturing method shown in FIG. 9;

[0036]FIG. 11 is a schematic perspective view illustrating the wiringmaterial in a state in which the wiring material is being used;

[0037]FIG. 12 is a schematic cross-sectional view illustrating acomposite material according to a fifth embodiment;

[0038]FIG. 13(a) is a schematic side view illustrating a state where thecomposite material of FIG. 12 is being used as the wiring material;

[0039]FIG. 13(b) is a side view illustrating a state where the wiringmaterial shown in FIG. 13(a) is located on a pad of the semiconductor;

[0040]FIG. 13(c) is a cross-sectional view illustrating the wiringmaterial shown in FIG. 13(a);

[0041]FIG. 13(d) is a schematic cross-sectional view illustrating thecomposite material shown in FIG. 12;

[0042]FIG. 14 is a schematic cross-sectional view illustrating amanufacturing method of a composite material according to a modifiedembodiment;

[0043]FIG. 15(a) is a schematic cross-sectional view illustrating acomposite material according to another modified embodiment;

[0044]FIG. 15(b) is a schematic cross-sectional view illustrating acomposite material according to another modified embodiment;

[0045]FIG. 16 is a schematic cross-sectional view illustrating apackaging module using a heat sink according to a prior art;

[0046]FIG. 17(a) is a schematic cross-sectional view illustrating acooling substrate according to a prior art in a state where a pair ofmetal plates are laid on each other with a wire fabric arranged inbetween;

[0047]FIG. 17(b) is a cross-sectional view illustrating the coolingsubstrate with the metal plates and the wire fabric shown in FIG. 7(a)being integrated;

[0048]FIG. 18 is a plan view illustrating a base material of a substratefor semiconductors according to another prior art;

[0049]FIG. 19 is an enlarged partial view of FIG. 17(b);

[0050]FIG. 20(a) is a schematic cross-sectional view illustrating thecooling substrate shown in FIG. 17(b); and

[0051]FIG. 20(b) is a schematic cross-sectional view illustrating acooling substrate according to another prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0052] A first embodiment of the present invention will now be describedwith reference to FIGS. 1(a) to 3.

[0053] FIGS. 1(a) and 1(b) show a composite material 11. The compositematerial 11 includes a first member, which is an expanded metal 12 inthe first embodiment, and a second member, which is a matrix metal 13 inthe first embodiment. The matrix metal 13 surrounds the expanded metal12. The expanded metal 12 is formed of a metal plate the coefficient oflinear expansion of which is less than or equal to 8×10⁻⁶/degreesCelsius. In the first embodiment, the expanded metal 12 is made ofinvar, which is an Fe and Ni based alloy including 36% Ni by weight. Thematrix metal 13 is a metal (copper is used in the first embodiment) thecoefficient of thermal conductivity of which is greater than or equal to200 W/(m×K). The expanded metal is formed by stretching a piece of metalplate having slits. The slits are expanded to form a wire fabric.

[0054] A manufacturing method of the composite material 11 will now bedescribed with reference to FIGS. 2 and 3. As shown in FIG. 2, theexpanded metal 12 is arranged between a pair of metal plates 14 made ofcopper. The expanded metal 12 and the metal plates 14 are then rolledand joined with each other to form the composite material 11. Morespecifically, as shown in FIG. 3, the metal plates 14 and the expandedmetal 12, which is arranged between the metal plates 14, are heated androlled by a pair of rollers 15. As a result, the metal plates 14 and theexpanded metal 12 are integrated into the composite material 11. In thiscase, the heating temperature is set such that the metal plates 14 willnot melt.

[0055] The coefficient of linear expansion and the coefficient ofthermal conductivity of the composite material 11 are determined byadjusting the size of the meshes of the expanded metal 12 or byadjusting the thickness of the metal plate 14. The composite material 11is manufactured in accordance with the intended purpose such that thecoefficient of linear expansion is approximately 5×10⁻⁶ to15×10⁻⁶/degrees Celsius.

[0056] The composite material 11 is used as a cooling substrate, onwhich semiconductors are mounted. The composite material 11 may be usedas a heat sink.

[0057] The first embodiment provides the following advantages.

[0058] (1) The expanded metal 12 is formed of the metal plate, thecoefficient of linear expansion of which is less than or equal to8×10⁻⁶/degrees Celsius, so as to suppress thermal expansion. Theexpanded metal 12 is then surrounded by the metal, the coefficient ofthermal conductivity of which is greater than or equal to 200 W/(m×K),so as to maintain the coefficient of thermal conductivity. The expandedmetal 12 and the metal are combined to form the composite material 11.Therefore, the composite material 11 has the coefficient of linearexpansion and the coefficient of thermal conductivity that are suitablefor the cooling substrate, on which electronic element such assemiconductors are mounted. Since the expanded metal 12 is used, thecomposite material 11 has superior heat conductivity and strength ascompared to a case where a wire fabric is used. Also, the manufacturingcost is reduced as compared to a case where holes are formed in a flatmetal plate by precision casting or punching.

[0059] (2) The expanded metal 12 is surrounded by the metal (matrixmetal 13), the coefficient of thermal conductivity of which is greaterthan or equal to 200 W/(m×K), to form the composite material 11.Therefore, the coefficient of thermal conductivity in the horizontaldirection is improved as compared to a structure in which part of theexpanded metal 12 is exposed at the surface of the composite material.

[0060] (3) In contrast to using the wire fabric, spaces are not easilyformed between the expanded metal 12 and the matrix metal 13. Thus, theheat conductivity and the strength are improved as compared to when thewire fabric is used. Also, the manufacturing cost is reduced as comparedto the case where holes are formed on a metal plate by precision castingor punching.

[0061] (4) The expanded metal 12 is made of invar, the coefficient oflinear expansion of which is approximately 1×10⁻⁶/degrees Celsius.Therefore, it is easy to obtain the composite material 11 having thecoefficient of linear expansion suitable for the cooling substrate thatis used for mounting electronic elements, such as semiconductors.

[0062] (5) The expanded metal 12 is rolled and joined while being heldbetween the metal plates 14, the coefficient of thermal conductivity ofwhich is greater than or equal to 200 W/(m×K). Therefore, the compositematerial 11 is manufactured without increasing the temperature as highas to melt the matrix metal. Thus, the manufacturing cost is reduced.

[0063] (6) Copper is used as the metal, the coefficient of thermalconductivity of which is greater than or equal to 200 W/(m×K). Thecoefficient of thermal conductivity of the copper is 390 W/(m×K), whichis relatively high. The copper is less expensive as compared to preciousmetals, but the copper improves the cooling performance of the compositematerial 11.

[0064] A manufacturing method of a composite material 111 according to asecond embodiment of the present invention will now be described withreference to FIG. 4. Among the method for manufacturing the compositematerial 111, the method for forming a matrix metal 13 differs from thatof the first embodiment shown in FIGS. 1 to 3. Like or the samereference numerals are given to those components that are like or thesame as the corresponding components of the embodiment of FIGS. 1 to 3and detailed explanations are omitted.

[0065] As shown in FIG. 4(a), the expanded metal 12 is arranged in amold 16. Then, a molten metal 17, which is copper in this embodiment, ispoured into the mold 16. As shown in FIG. 4(b), a molded body 18 isrolled by the rollers 15 to a predetermined thickness to form thecomposite material 111. The molded body 18 is removed from the mold 16while the temperature of the molded body 18 is considerably high, orbefore the molded body 18 is completely cooled. In this case, the moldedbody 18 need not be heated when rolled by the rollers 15.

[0066] The second embodiment provides the following advantages inaddition to the advantages (1) to (4), and (6) of the first embodimentshown in FIGS. 1 to 3.

[0067] (7) The molten metal 17 is poured into the mold 16, in which theexpanded metal 12 is arranged, to form the molded body 18. The moldedbody 18 is then rolled. Therefore, the matrix metal 13 easily surroundsand adheres to the expanded metal 12.

[0068] (8) The rollers are only required to adjust the thickness of themolded body 18 and need not join the metal plates 14. Thus, the pressureof the rollers need not be great.

[0069] A composite material 211 according to a third embodiment will nowbe described with reference to FIGS. 5(a) to 7. The composite material211 of the third embodiment differs from the embodiments of FIGS. 1 to4(b) in that several expanded metals 12 are used and parts of theexpanded metals 12 are exposed on the surfaces of the composite material211. Like or the same reference numerals are given to those componentsthat are like or the same as the corresponding components of theembodiments of FIGS. 1 to 4(b) and detailed explanations are omitted.

[0070] As shown in FIGS. 5(a) and 5(b), the composite material 211includes several expanded metals 12 (two are provided in the thirdembodiment) and the matrix metal 13. The expanded metals 12 are locatedon the front and rear surfaces of the composite material 211, and thematrix metal 13 is located between the expanded metals 12 and in meshes12 a of the expanded metals 12.

[0071] A method for manufacturing the composite material 211 constitutedas described above will be described with reference to FIGS. 6 and 7. Inthe manufacturing method of the third embodiment, as shown in FIG. 6,the metal plate 14 made of cupper is rolled and joined while being heldbetween two expanded metals 12 to form the composite material 211. Thatis, as shown in FIG. 7, the metal plate 14 is heated and rolled with therollers 15 while being arranged between two expanded metals 12.Therefore, metal forming the metal plate 14 enters the meshes 12 a ofthe expanded metals 12. After being pressed by the rollers 15, thematrix metal 13 is integrated with the expanded metals 12 to form thecomposite material 11 in a state in which the matrix metal 13 is locatedbetween two expanded metals 12 and in the meshes 12 a. The temperatureis set not to be as high as to melt the matrix metal 14.

[0072] The third embodiment provides the following advantages inaddition to the advantages (1), (3), (4), and (6) of the firstembodiment of FIGS. 1 to 3.

[0073] (9) Since the expanded metals 12 are exposed on the front andrear surfaces of the composite material 211, the thermal expansion atthe vicinity of the front and rear surfaces of the composite material211 is more effectively suppressed as compared to a case where theentire expanded metal 12 is surrounded by the metal, the coefficient ofthermal conductivity of which is greater than or equal to 200 W/(m×K).

[0074] (10) When manufacturing the expanded metal 12, the thinner theexpanded metal 12 is the easier the fine mesh 12 a is made. Therefore,when the volume ratio of the expanded metal 12 and the matrix metal 13is the same, the structure in which several expanded metals 12 are usedpermits the meshes 12 a to be easily made small as compared to astructure in which one expanded metal 12 is used. As a result, thecomposite material 211 that has uniform quality is easily obtained.

[0075] A composite material 221 according to a fourth embodiment willnow be described with reference to FIGS. 8(a) to 11. The compositematerial 221 of the fourth embodiment differs from the embodiments ofFIGS. 1 to 7 in that the composite material 221 is formed to be suitablefor wiring material of semiconductors.

[0076] As shown in FIGS. 8(a) to 8(c), the composite material 221includes a plate-shaped conductive member 22 and an expansionsuppressing portion 23, which is located at the end of the conductivemember 22. The conductive member 22 is a copper foil. The thickness ofthe copper foil is formed to be, for example, some μm to 300 μm, or morepreferably, some um to some tens of μm depending on the conditions ofusage.

[0077] The expansion suppressing portion 23 includes a first member,which is an expanded metal 24, and a second member, which is a metal thecoefficient of thermal conductivity of which is greater than or equal to200 W/(m×K). The expanded metal 24 is formed by a metal plate, thecoefficient of linear expansion of which is less than or equal to8×10⁻⁶/degrees Celsius. The second member is filled in the mesh of theexpanded metal 24. The expanded metal 24 suppresses the thermalexpansion and the metal filled in the mesh maintains the coefficient ofthermal conductivity. Copper, which is the same material as theconductive member 22, is used for the metal, the coefficient of thermalconductivity of which is greater than or equal to 200 W/(m×K). Theexpanded metal 24 is made of invar.

[0078] The composite material 221 may be formed into a shape of wiringmaterial from the beginning (for example, the shape shown in FIG. 8(c)).More preferably, as shown in FIG. 8(a), the composite material 221 isformed into a shape in which units that are used as wiring material areintegrated as one body. The composite material 221 is then cut into apredetermined width to be used. In this case, the composite material 221is preferable in the aspects of productivity, storage, and handlingperformance.

[0079] The composite material 221 is manufactured by performingresistance welding while crimping the plate-shaped expanded metal 24 ofa predetermined size to the end of the plate-shaped conductive member 22of a predetermined size. For example, as shown in FIG. 9, seam weldingis used in a suitable manner. In this case, welding is performedlinearly while rotating a pair of disk-like welding electrodes 25 a, 25b, which are able to apply pressure and conduct electricity. In themethod shown in FIG. 9, resistance welding is performed when a portionwhere the conductive member 22 overlaps the expanded metal 24 passesbetween the welding electrodes 25 a and 25 b. As a result, theconductive member 22 and the expanded metal 24 are joined with eachother with part of the conductive member 22 filled in the mesh 24 a ofthe expanded metal 24. Accordingly, the composite material 221, whichhas the expansion suppressing portion 23 at the end of the conductivematerial 22, is manufactured.

[0080] Instead of performing seam welding at the overlapped portion ofthe plate-shaped conductive member 22 and the expanded metal 24, theconductive member 22 that is wound into a coil and the expanded metal 24that is also wound into a coil may be used. The composite material 221welded through the welding electrodes 25 a and 25 b may then be woundinto a coil as shown in FIG. 10. In this case, the productivity isincreased and handling of the composite material 221 is facilitated ascompared to a case where the plate-shaped conductive member 22 and theexpanded metal 24 are used to manufacture the composite material 221.

[0081] The composite material 221 is, for example, used as a wiringmaterial 33 of a semiconductor in a suitable manner as shown in FIG. 11.FIG. 11 is a partial schematic perspective view of an IGBT (insulatedgate bipolar transistor) module constituting the semiconductor. Aninsulating plate 27 is secured to a heat sink 26. An IGBT element 28 anda diode element 29 are mounted on the insulating plate 27. An emitterelectrode 30, a gate electrode 31, and a collector electrode 32 are alsolocated on the insulating plate 27. An emitter pad of the IGBT element28, which serves as the semiconductor element, is connected to one endof the wiring material 33 by diffusion bonding. The other end of thewiring material 33 is connected to an emitter electrode 30. Theexpansion suppressing portion 23 is formed to have substantially thesame size as the IGBT element 28. With regard to the composite material221, which is used as the wiring material 33, the end of the compositematerial 221 close to the expansion suppressing portion 23 correspondsto the emitter pad, and the conductive member 22 is joined to theemitter pad. A hole is formed in the wiring material 33 at a portioncorresponding to a gate pad of the IGBT element 28. The gate pad isconnected to the gate electrode 31 with a wire 34.

[0082] The diode element 29 and the emitter electrode 30 are connectedto each other with the wiring material 33. The expansion suppressingportion 23 is formed to have substantially the same size as the diodeelement 29. The end of the wiring material 33 that is close theexpansion suppressing portion 23 corresponds to the diode element 29,and the conductive member 22 is joined to the diode element 29.

[0083] To facilitate illustration, the composite material 221 shown inFIGS. 8(a) to 8(c) and the wiring material 33 (composite material 221)shown in FIG. 11 are drawn with different area ratio between theconductive member 22 and the expansion suppressing portion 23. Thethicknesses of the conductive member 22 and the expansion suppressingportion 23 are also exaggerated.

[0084] The fourth embodiment provides the following advantages.

[0085] (11) The bonding pad of the semiconductor element or thesemiconductor element is connected to the electrode (emitter electrode30) with the plate-shaped wiring material 33. Therefore, the pad or thesemiconductor element is joined to the electrode in a manner that doesnot apply great stress on the pad or the semiconductor element. Thus,the element is prevented from being damaged. This improves the coolingperformance of the wiring material 33 as compared to wires, and reducesthe thermal stress applied to the joint portion, which preventsdeterioration of the joint portion.

[0086] (12) The expansion suppressing portion 23 is formed at a portionof the wiring material 33 that corresponds to the semiconductor element,which has a small thermal expansion. Therefore, the thermal expansion ofthe conductive member 22 at the above portion is suppressed, whichsuppresses damages on the wiring material 33 or the semiconductorelement due to the heat generated during operation of the semiconductor.

[0087] (13) The expansion suppressing portion 23 includes the expandedmetal 24, which is formed by a metal plate the coefficient of linearexpansion of which is less than or equal to 8×10⁻⁶/degrees Celsius, andthe metal the coefficient of thermal conductivity of which is greaterthan or equal to 200 W/(m×K) filled in the mesh 24 a of the expandedmetal 24. Therefore, the expansion suppressing portion 23 also has highcooling performance.

[0088] (14) The composite material 221 is formed into a shape in whichseveral units used as the wiring material 33 are integrated. Thecomposite material 221 is then cut into the predetermined width whenused as the wiring material 33. Therefore, the composite material 221 ispreferable in the aspects of productivity, storage, and handlingperformance. Also, the manufacturing cost is reduced as compared to acase where the composite material 221 is manufactured to have the sizeof the wiring material 33 from the beginning.

[0089] (15) The composite material 221 is manufactured by performingresistance welding, or more preferably, seam welding, with theconductive member 22 overlapped with the expanded metal 24.

[0090] (16) When the composite material 221 is manufactured continuouslyby seam welding using the conductive member 22 that is wound into a coiland the expanded metal 24 that is wound into a coil, the productivity isincreased and the handling is facilitated.

[0091] A composite material 321 according to a fifth embodiment will nowbe described with reference to FIGS. 12 to 13(d). The composite material321 of the fifth embodiment is the same as the composite material 221 ofthe fourth embodiment shown in FIGS. 8(a) to 11 in that the compositematerial 321 is used as the wiring material in a suitable manner.However, the composite material 321 of the fifth embodiment differs fromthe composite material 221 of the fourth embodiment shown in FIGS. 8(a)to 11 in that an insulation member 35 is laminated on the expansionsuppressing portion 23. Like or the same reference numerals are given tothose components that are like or the same as the correspondingcomponents of the fourth embodiment of FIGS. 8(a) to 11 and detailedexplanations are omitted.

[0092] As shown in FIG. 12, the composite material 321 includes theconductive member 22, the expansion suppressing portion 23, and theinsulation member 35. The insulation member 35 is made of rubber in thefifth embodiment, and silicon rubber is used as the rubber. Thecomposite material 321 is manufactured by arranging the expanded metal24 and the insulation member 35 on the end of the plate-shapedconductive member 22 in layer, and applying pressure on the side of theinsulation member 35. When the insulation member 35 is pressurized, thematerial of the conductive member 22 and the insulation member 35 arefilled in the mesh 24 a of the expanded metal 24. As a result, theconductive member 22, the expansion suppressing portion 23, and theinsulation member 35 are integrated.

[0093] The composite material 321 is formed into a shape in whichseveral units used as the wiring material are integrated. In addition toa structure in which the composite material 321 is cut into thepredetermined width to be used, the composite material 321 may bemanufactured to be the wiring member during wiring. For example, asshown in FIG. 13(a), the expanded metal 24 and the insulation member 35,which are formed into a predetermined size, are laminated on the end ofthe conductive member 22, which is formed into the size of the wiringmaterial. The expanded metal 24 and the insulation member 35 aretemporarily secured to the conductive member 22 with a small amount ofadhesive. The end of the wiring material on which the expanded metal 24is located is arranged on a pad 36 of the semiconductor element to bejoined as shown in FIG. 13(b). In this state, pressure and ultrasonicwave are applied from the side of the insulation member 35. As a result,the conductive member 22 is joined with the pad 36. The conductivemember 22 and the insulation member 35 are also joined with the expandedmetal 24 with part of the conductive member 22 being filled in the mesh24 a of the expanded metal 24 and part of the insulation member 35 beingfilled in the mesh 24 a of the expanded metal 24. As a result, theexpansion suppressing portion 23 is joined to the end of the conductivemember 22, and the insulation member 35 is joined on the expansionsuppressing portion 23 to form the composite material 321. FIG. 13(c) isa cross-sectional view of FIG. 13(a), and FIG. 13(d) is across-sectional view of the composite material 321.

[0094] The fifth embodiment provides the following advantages inaddition to the advantages (11) and (12) of the fourth embodiment shownin FIGS. 8(a) to 11.

[0095] (17) The composite material 321 is formed utilizing great loadapplied to the wiring material when joining the wiring material to thesemiconductor element. Therefore, as compared to a case where thecomposite material 321 that is manufactured in advance is used as thewiring material, the energy required for manufacturing the compositematerial 321 is reduced. Also, the manufacturing cost is further reducedsince the composite material 321 is formed at the room temperature.

[0096] (18) The insulation member 35 is joined to the conductive member22 via the expanded metal 24 such that the insulation member 35 facesthe conductive member 22 of the expansion suppressing portion 23.Therefore, means for retaining the insulation of the wiring material isnot particularly required when joining the wiring material with thesemiconductor element. This facilitates the procedure.

[0097] (18) Since the insulation member 35 is made of rubber, shock isnot easily applied to the expansion suppressing portion 23. Also, sincesilicon rubber is used as the rubber, the insulation member 35 hassuperior heat resistance and does not deteriorate easily by the heatgenerated during operation of the semiconductor.

[0098] (20) Since the insulation member 35 is made of silicon rubber andis pressed against the conductive member 22 that is filled in the mesh24 a, the cooling performance of the expansion suppressing portion 23 ismaintained.

[0099] It should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention. Particularly, itshould be understood that the invention may be embodied in the followingforms.

[0100] As shown in FIG. 14, the expanded metal 12 that is formed intothe thickness of the product may be arranged in a mold 416 having acavity the shape of which corresponds to the composite material 411 as aproduct. The molten metal 17 may then be poured into the mold 416 tomanufacture the composite material 411. In this case, the compositematerial 411 is manufactured without the rolling, which facilitates themanufacturing of the composite material 411. A predetermined pressuremay be applied after pouring the molten metal into the mold 416. In thiscase, the molten metal 17 easily enters the opening portions even thoughthe expanded metal 12 has small opening portions.

[0101] Instead of arranging the expanded metal 12 in the mold 16, 416and pouring the molten metal 17 into the mold 16, 416, the expandedmetal 12 may be soaked in a metal bath. In this case, after beingremoved from the metal bath, the expanded metal 12 is rolled to form thecomposite material. Alternatively, instead of being rolled, the expandedmetal 12 may be externally machined to form the composite material.

[0102] In the third embodiment shown in FIGS. 5(a) to 7, three or moreexpanded metals 12 may be used. In this case, the matrix metal 13 existsbetween the expanded metals 12 and in the mesh 12 a of each expandedmetal 12. With the structure in which several expanded metals 12 areused, the thickness of each expanded metal 12 can be made thin ascompared to a case where one expanded metal 12 is used when the volumeratio of the expanded metal 12 to the entire volume of the compositematerial 211 is the same. As a result, the fine mesh 12 a is easilyformed and the composite material 211 that has uniform quality is easilymanufactured.

[0103] The composite material 11 of FIG. 1(b) and the composite material111 of FIG. 4(b) may use several expanded metals 12.

[0104] In the structure in which several expanded metals 12 are used,the expanded metals 12 need not be made of the same material. However,the expanded metals 12 that are arranged symmetrical with respect to thesurface that lies along the center of each composite material 11, 111,211 of FIGS. 1(a) to 7 in the width direction are preferably made of thesame material. In this state, generation of warp on the compositematerial 211 is suppressed even if the coefficient of thermal expansiondiffers due to the difference of materials.

[0105] The composite material 221 of FIGS. 8(a) to 8(c) and thecomposite material 321 of FIG. 12, which are suitable for the wiringmaterial, need not have a structure in which part of the conductivemember 22 is filled in the mesh 24 a of the expanded metal 24 withapplication of pressure. Instead, the expansion suppressing portion 23may be formed with the composite material in which metal having highthermal conductivity is filled in the mesh 24 a of the expanded metal inadvance. Then, the composite material may be joined to the end of theconductive member 22. As a composite material 421 shown in FIG. 15(a),the expansion suppressing portion 23 may be joined to the conductivemember 22, and a metal plate 37 the coefficient of thermal conductivityof which is greater than or equal to 200 W/(m×K) may be joined to aposition opposite to the conductive member 22 with respect to theexpansion suppressing portion 23. Further, as a composite material 521shown in FIG. 15(b), only the expansion suppressing portion 23 may bejoined to the conductive member 22.

[0106] The metal plate 37 shown in FIG. 15(a) may be formed of metalthat is the same as the conductive member 22 or different metal. Themetal that is filled in the mesh 24 a of the expanded metal 24 may alsobe the same as the conductive member 22 or different metal. A preferablemetal other than copper is aluminum.

[0107] When manufacturing the composite material 221 of FIGS. 8(a) to8(c) by seam welding, one of the electrodes may be plate-shaped, and theoverlapped portion of the conductive member 22 and the expansionsuppressing portion 23 may be located on the plate-shaped electrode.Then, the conductive member 22 and the expansion suppressing portion 23may be joined by rotating and shifting a disk-like welding electrode.

[0108] For the manufacturing method of the composite material 221 ofFIGS. 8(a) to 8(c), press molding, such as hot press molding and coldpress molding, or a rolling method may be employed.

[0109] The insulation member 35 may be made of resin.

[0110] In the fifth embodiment of FIGS. 12 to 13(d), pressure is appliedwhile temporarily securing the conductive member 22, the expanded metal24, and the insulation member 35 with adhesive. Instead, the conductivemember 22 and the expanded metal 24 may be temporarily secured withadhesive, and the insulation member 35 may be located on the adheredconductive member 22 and the expanded metal 24. Then, pressure may beapplied to the insulation member 35.

[0111] The matrix metal 13 may be a metal the coefficient of thermalconductivity of which is greater than or equal to 200 W/(m×K). Forexample, aluminum based metal or silver may be used. The aluminum basedmetal refers to aluminum and aluminum alloy. The coefficient of thermalconductivity of the aluminum based metal is low as compared to that ofthe copper. The melting point of the aluminum based metal (aluminum) is660 degrees Celsius, which is significantly lower than the melting pointof the copper, which is 1085 degrees Celsius. Thus, the meltingtemperature of the metal is decreased. This results in the reduction ofthe manufacturing cost as compared to the copper. Aluminum based metalis also preferable in view of weight reduction.

[0112] The expanded metal 12 may be formed of any metal the coefficientof linear expansion of which is less than or equal to 8×10⁻⁶/degreesCelsius. For example, other invar alloy such as super invar, stainlessinvar, or fernico, which is an alloy of 54% Fe by weight, 31% Ni byweight, and 15% Co by weight, the coefficient of linear expansion ofwhich is 5×10⁻⁶/degrees Celsius, may be used.

[0113] In the manufacturing method of the composite material 11, 111,211 shown in FIGS. 1(a) to 7, the adhesion process need not beperformed. The composite material 11 may be manufactured by heattreatment after cold rolling.

[0114] The composite materials 11, 111, 211 may be used as coolingsubstrate used for purposes other than mounting semiconductors.

[0115] The mold 16, 416 may be made of ceramics.

1. A plate-shaped composite material characterized by: a first member,wherein the first member is an expanded metal made of metal plate,wherein the coefficient of linear expansion of the metal plate is lessthan or equal to 8×10⁻⁶/degrees Celsius, and wherein the first membersuppresses thermal expansion of the composite material; and a secondmember, wherein the second member is formed of metal, wherein thecoefficient of thermal conductivity of the metal is greater than orequal to 200 W/(m×K), and wherein the second member maintains thecoefficient of thermal conductivity of the composite material.
 2. Thecomposite material according to claim 1, characterized in that thesecond member surrounds the first member.
 3. The composite materialaccording to claim 2, characterized in that the second member is one ofa pair of second members, wherein the first member is arranged betweenthe second members, and wherein the first and second members are rolledand joined with each other.
 4. The composite material according to claim2, characterized in that the second member is melted and poured into amold in which the first member is arranged to form a molded body, andwherein the molded body is rolled to have a predetermined thickness,thereby forming the composite material.
 5. The composite materialaccording to claim 2, characterized in that the composite material isobtained by soaking the first member in a metal bath of the meltedsecond member, and then removing the first member from the metal bath.6. The composite material according to claim 1, characterized in thatthe first member is one of a pair of first members, and wherein thesecond member is arranged between the first members.
 7. The compositematerial according to claim 1, characterized in that at least two firstmembers are used, wherein each first member is located on one of frontand rear surfaces of the composite material, and wherein the secondmember exists between the first members and in meshes of the firstmembers.
 8. A composite material characterized by a plate-shapedconductive member having an end and a plate-shaped expansion suppressingportion located at the end of the conductive member, wherein theexpansion suppressing portion includes: a first member, wherein thefirst member is an expanded metal made of metal plate, wherein thecoefficient of linear expansion of the metal plate is less than or equalto 8×10⁻⁶/degrees Celsius; and a second member, wherein the secondmember is formed of metal, wherein the coefficient of thermalconductivity of the metal is greater than or equal to 200 W/(m×K),wherein the first member suppresses the thermal expansion of thecomposite material, and wherein the second member maintains thecoefficient of thermal conductivity of the composite material.
 9. Acomposite material characterized by a plate-shaped conductive memberhaving an end and a plate-shaped expansion suppressing portion locatedat the end of the conductive member, wherein the expansion suppressingportion includes: a first member, wherein the first member is anexpanded metal made of metal plate, wherein the coefficient of linearexpansion of the metal plate is less than or equal to 8×10⁻⁶/degreesCelsius; and a second member, wherein the second member is formed ofmetal, wherein the coefficient of thermal conductivity of the metal isgreater than or equal to 200 W/(m×K), wherein at least one of theconductive member and the second member is filled in meshes of the firstmember and laminated on the first member.
 10. The composite materialaccording to any one of claims 1 to 9, characterized in that the secondmember is copper or aluminum.
 11. The composite material according toany one of claims 1 to 10, characterized in that the first member is aninvar or an Fe—Ni alloy, which has substantially the same coefficient oflinear expansion as the invar.
 12. A composite material characterized bya plate-shaped conductive member having an end and an expansionsuppressing portion located at the end of the conductive member, whereinthe expansion suppressing portion includes a plate-shaped insulationmember and an expanded metal made of a metal plate, wherein thecoefficient of linear expansion of the metal plate is less than or equalto 8×10⁻⁶/degrees Celsius, and wherein part of the conductive member isfilled in meshes of the expanded metal.
 13. The composite materialaccording to claim 12, characterized in that the insulation member ismade of rubber.
 14. The composite material according to claim 12 or 13,characterized in that the expanded metal is an invar or an Fe—Ni alloy,which has substantially the same coefficient of linear expansion as theinvar.
 15. A manufacturing method of a composite material characterizedby: forming a first member from an expanded metal made of a metal plate,wherein the coefficient of linear expansion of the metal plate is lessthan or equal to 8×10⁻⁶/degrees Celsius; and surrounding the firstmember with a second member, wherein the second member is made of metal,and wherein the coefficient of thermal conductivity of the metal isgreater than or equal to 200 W/(m×K).
 16. The method according to claim15, characterized in that the second member is one of a pair of secondmembers, wherein the surrounding includes rolling the second memberswith the first member located in between, and joining the first memberwith the second members.
 17. The method according to claim 15,characterized in that the surrounding includes: arranging the firstmember in a mold; preparing a molded body by melting the second memberand pouring the melted second member into the mold; and rolling themolded body to have a predetermined thickness.
 18. The method accordingto claim 15, characterized in that the surrounding includes: soaking thefirst member in a metal bath of the melted second member; and removingthe first member from the metal bath.
 19. A manufacturing method of acomposite material characterized by: laminating an expanded metal and arubber sheet at an end of a plate-shaped conductive member, wherein theexpanded metal is formed of a metal plate, wherein the coefficient oflinear expansion of the metal plate is less than or equal to8×10⁻⁶/degrees Celsius, and wherein the expanded metal suppressesthermal expansion of the composite material; applying pressure to therubber sheet and filling the conductive member and the rubber sheet inmeshes of the expanded metal; and surrounding the expanded metal with ametal to maintain the coefficient of thermal conductivity of thecomposite material, wherein the coefficient of thermal conductivity ofthe metal is greater than or equal to 200 W/(m×K).